In recent years, the audio-visual age (that is so-called the AV age) has come and, accordingly, the demands for packaged visual media and the production thereof have been increased. In particular, a large quantity of blank video products and video products recorded music, motion pictures, animations and dramatic stages have been consumed every day as the commercial articles or the rental articles.
However, in the video industry where the video equipments are getting popularized, there are some people, who are not authorized by any lawful copyright owner, dub the contents of already recorded video softs in and they produce and sell a large quantity of the so-called pirated edition.
There have been strong requests in the video industry for forbidding any pirated edition to circulate. Accordingly, there are demands for technical means for forbidding the pirated editions to circulate so as to protect the benefits of the whole video industry.
The technical means for forbidding the pirated editions to circulate include, for example, a means in which a hologram (i.e., a seal) is utilized, another means in which a front cover so-called a lid covering the whole surface of a tape cassette is colored or a further means in which any dubbing is made impossible by applying a separate signal to an image signal.
In the above-given means, however, the pirated editions can not fully be forbidden, because any pirated edition producers can readily imitate. In addition, it costs more expensive and there may be some instances where the image quality of an original soft may be spoiled.
On the other hand, Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP OPI Publication) No.62-231426/1987 discloses a technique in which a magnetic layer is separated into two layers, the upper and lower layer, and a pigment or a dye is contained in the lower layer so that the lower layer can be discriminated by the color from the upper layer. This technique claims that the coating defects or coating unevenness on the upper layer can be discriminated by the colored contents of the lower layer. It is, however, not clear whether the discrimination can be made by the color of the lower layer for the purpose of forbidding the above-mentioned pirated edition. Further, in this patent publication, there is neither any indication nor suggestion of any technical idea that the lower layer is colored with the purpose of forbidding any pirated edition.
Still further, there may be some instances where the contrast of the upper layer may be deteriorated by mixing the color of a pigment or the like contained in the lower magnetic layer with the color (which is usually in dark-brown) of the magnetic powder of the same lower magnetic layer and, in addition, the electromagnetic conversion characteristics of the lower layer may be affected by a large amount of the pigment are contained in the magnetic layer. The above-mentioned cases fall similarly under the case of a medium having a light tightness provided by containing carbon black and so forth in a single-layered magnetic layer.